If you set up your projector correctly you should only be using the lens shift adjustment and not the keystone adjustment.

What is your setup::

- Is the projector centered horizontally with the screen or is it positioned to the left to right of the screen center (if so how much is it offset from the screen's center)?

- Is the projector ceiling mounted or is it table or shelf mounted?

- what is the distance from the screen to the front of the projector?

- What is the vertical position of the projector relative to the screen (for example how far above or below the top edge of the screen is the projector located).

The projector should be level (not tilted up or down) and the front of the projector should be parallel with the screen (not rotated right or left) then the projector's lens shift adjustments should be used to center the image on the screen.

Keystone should never be used in a HT environment with a permanently installed projector. Keystone is a though back from the days of table top presentation projection where the built in offset or lens sift was insufficient. The screen was up on a stage or high on a wall and the projector was on a desk or table. The image was trapezoid and looked bad. Keystone digitally compressed/stretched/combined pixels to make the image square. You be the judge, compressed processed pixels with keystone.. does it change the image..

Keystoning is caused by the projector lens not being parallel to the screen.. This makes various sides of the lens further or closer to the screen than the opposite side. Keystone correction uses very difficult scaling vs easy scaling to make the image rectangular again. This scaling softens the image making it really degraded. Its night and day. when Ron says don't tilt the projector up or down but make it level, he is really saying make the lens parallel to the screen surface. the is as Ron says also includes twisting the lens left right so that it is completely parallel. Use lens shift to center the image vertically and horizontally. The election polls should be closed. No one who cares about image quality would use electronic keystone correction.